1. Field of the Invention
The present invention relates to an imaging optical system, and more particularly, to an imaging optical system installed in a mobile communications terminal and a personal digital assistant (PDA) or utilized in a surveillance camera and a digital camera.
2. Description of the Related Art
Recently, with regard to an image pickup system, studies have been conducted on camera modules for telecommunication terminals, digital still cameras (DSCs), camcorders, and personal computer (PC) cameras which are attached to personal computers as imaging devices. Here, an image-forming lens system is the most important component of such an image pickup system in obtaining an image.
The lens system needs to be high-performing in terms of resolution and image quality, thus complicating a lens configuration. However, such structural and optical complexity leads to an increase in size, posing a difficulty to the realization of compactness and thinness in the lens system.
For example, a camera module should necessarily be miniaturized to be installed in a mobile phone more efficiently. Also, an image sensor such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) employed in the camera module has an increasingly higher resolution, with a concurrent decrease in pixel size. The lens system included in the camera module needs to be smaller-sized and thinner while attaining high resolution and superior optical capabilities.
In the case of using a 3-megapixel image sensor (CCD or CMOS), only three or less sheets of lenses may be arranged to satisfy optical capabilities and miniaturization. However, in the case that three or less sheets of lenses are applied to a 5 or more-megapixel image sensor (CCD or CMOS), each of the lenses should be increased in refractive power, and accordingly this poses a difficulty to machininability. For this reason, it is difficult to satisfy both requirements of high performance and miniaturization at the same time. Also, even though four or more sheets of lenses are employed, if those lenses are formed of spherical lenses, a total length of the optical system increases, and accordingly miniaturization is not ensured.
Therefore, there has been a demand for a lens system for a camera module which can be subminiaturized, yet realize high performance optical capabilities.